Growing Organic Potatoes

POTATO DEFINITIONS

Seed Potatoes - approx. 2" x 2" potato chunks with at least 1 or 2 "eyes."

Potato Seeds - growing potatoes from actual seed which is more difficult; most gardeners simply plant seed potatoes.

Spuds - nickname for potatoes - derived from the Latin "spad" which means sword. Our word "spade" comes from this word which is a "sword which is stuck into the ground" to open the hole for the potato. Sometime in the 19th century "spud" - an Irish digging implement used to plant potatoes - and "potato" became synonymous. Don't ask me...I'm only part Irish!

WHEN TO PLANT

In Northern areas, you can begin planting and growing seed potatoes directly in the garden 14-21 days before the last frost date.

Potatoes can withstand a light frost, and even if the plants wilt and turn black with a heavier frost, the plants will come back (this happened to us last year).

You can begin growing most varieties of potatoes in late March or April; if you plant too early in the spring you run the risk of your seed potatoes rotting before they grow.

Last year I made the mistake of planting our potatoes too early, and it really stunted their growth. Our Ukrainian neighbors planted around mid-April, and their potatoes came up before ours did! And they had a much better harvest.

Late season potatoes may be planted as late as July in Northern climates. These late season varieties store better as well.

You can grow both red-skinned and white-skinned potatoes as early and late crops.

In Southern areas, you can begin planting and growing in February or March. Temperatures usually stay above freezing in many areas of the "deep south" (Southern parts of GA, AL, MS, LA, TX, and the entire state of Florida). In these areas you can often plant potatoes by mid-January, and another crop in mid-to-late September.

Depending on your growing climate, potatoes reach maturity around 3 to 4 months.

WHERE TO PLANT

Potatoes should be planted in an area that receives at least six hours of full sunlight daily.

If you're converting lawn to garden area, it is best to avoid planting potatoes in the new garden area for at least the first year as they may be assaulted by grubworms.

Potatoes prefer well-drained soil with moderate quantities of organic matter and sand.

Don't add large amounts of manure to your soil as it causes scabs on your potatoes - this happened to us a few years back.

PREPARING YOUR SOIL

Potatoes grow best if the pH level of your soil is around 4.8 to 5.5; they'll usually do OK even up to 6.5, although they may have more scabbing.

If your soil has a pH above 6.0, you can purchase potato varieties that are scab-resistant.

Potatoes require a decent amount of potassium and phosphate which is typical of root crops.

Trenching:

1) Dig a trench about 12" deep and 18" wide.

2) Mix 2 - 3 inches of compost in with about half of the dirt; Note: The University of Maine concluded, after a multi-year study, that adding 10 tons of compost per acre over the period of the study did increase the crop yield.

3) Mix another 2 - 3 inches of compost in with the dirt on the side of the trench; if you need to add potassium to your soil, mix a good organic source such as bone meal, which strengthens the roots.

4) The center of the trench will become your row - space rows about 30 to 36 inches apart.

5) Add an organic nitrogen fertilizer into the soil on the side of the trench if needed.

6) Remove any larger rocks as they'll deform your potatoes.

Now you're ready to plant!

SEED VARIETIES

To start your potato patch, decide how many pounds of potatoes you would like to harvest.

Five pounds of seed potatoes will yield between 45 and 70 lbs. of potatoes and will require a garden area of about 10 x 12 feet.

Plant at least two varieties (I like a red variety and Yukon Golds, a white variety) .

Think about planting both an early maturing (reds) and a medium or late maturing variety (white).

SEEDS AND GERMINATION

Potatoes germinate at a low soil temperature of 45°, but germinate best at a temperature of about 55° to 65°F.

Growing potatoes at a soil temperature of 45° will work OK, but grow best in the temperature range of 55° to 80°F.

Potatoes stop forming if the soil temperature reaches 80°F; to prevent soil from getting too warm, layer 3 to 4 inches of straw or other organic mulch around your potatoes to keep the soil cool and the weeds under control.

It takes about 2 to 4 weeks to see potato seedlings emerge from your soil, depending on the soil temperature.

Potatoes require significant light and moisture to germinate well.

Jenny's Tip #1: If you're planting early potatoes, you can sprout your potatoes before planting. This could bring your potato harvest two or three weeks earlier. To sprout your potatoes, lay your seed potatoes in a tray in sunlight or a greenhouse until the sprouts are no longer than an inch. Carefully plant the sprouted potatoes being careful not to break the sprouts off.

DIRECT PLANTING IN YOUR GARDEN

When you're growing potatoes, decide how many pounds you'll want to harvest; our family of six eats about 300lbs. per year.

You'll typically get between 8 and 14 pounds of potatoes per pound you plant; it'll take about 8 to 10 lbs of seed potatoes per every 100 feet of potatoes you plant. Again, using our family as an example, we'd plant about 35 to 40 lbs. of potatoes at the most, although last year our yield was about 12 lbs. to every pound of potatoes planted, so we might want to plant maybe 30 lbs., or about three 80 foot rows.

Note: Planting potatoes from the grocery store is not recommended; they are treated to keep from sprouting and you don't know what diseases they might bring into your area.

Prior to planting your seed potatoes, cut them into pieces with one or two eyes (preferably two) and let them cure in a warm, dry place for at least 12 hours (24 is even better, but if you're like me, you want to get those little spuds in the ground!).

After your potatoes are cured, place them in the trench outlined in the "Preparing Your Soil" area above; at least one "eye" should be pointing up.

If you've prepared your trench well, you should have loose, well-drained soil to plant your potatoes in; place one of your cut seed potatoes every 10 to 12 inches.

Take the remaining soil that's piled on the side of the trench and cover the tops of your potatoes with 3 to 4 inches of soil.

Make sure the soil is very moist.

Straw Potatoes: An Alternate Planting Method

"Planting" potatoes on the top of the ground and covering with straw has been cleverly named "straw potatoes."

Till or loosen your soil, adding compost similar to the previous method. Tilling the compost and bonemeal into the soil works well.

Lay the potatoes on top of the ground 10 to 12 inches apart the same as you would trenched potatoes, then cover with 4 to 6 inches of straw.

Within a couple weeks you should see potato seedling popping up through the straw. Add straw around the plants during the season if the straw cover gets to thin.

Straw potatoes have very few weeds, especially if you are able to procure clean barley straw. Pull the few weeds that do emerge.

Use of straw helps keep the soil temperature below 80°F even on the hottest summer days, reducing water loss.

If you want to enter your potatoes into the county fair, using the strawing method for growing potatoes will produce a more physically attractive spud than one grown in the dirt.

GROWING

When your potato seedlings reach about 6" in height, mound another 3" of soil around the base of the plant to keep the potatoes from being exposed to the sun. Do this every couple of weeks until the potatoes flower.

This prevents your potatoes from turning green; a potato that has turned green contains a bitter-tasting alkaloid that is mildly poisonous.

As previously mentioned, once your potato seedlings have reached about 6" in height, you can either mound soil around your plants or, and this is my preferred method, you can add about 3 to 4 inches of clean straw mulch around your plants.

Mulching helps maintain a more even and lower soil temperature which is conducive to growing potatoes; and it helps keep the weeds under control.

One additional feature of straw mulch is that it makes it difficult for the Colorado Potato Beetle larvae to get to your potato plants.

When weeding your potatoes, pull the weeds by hand as potatoes grow very close to the surface of the soil and tilling might damage the young tubers.

Avoid heavy fertilization of potatoes which encourages excessive foliage growth and delays tuber growth. Most of the fertilizing should be done before the potatoes are planted.

Jenny's Tip #2: This past year we discovered a liquid organic leaf spray fertilizer called Organic Garden Miracle™ (OGM). This leaf spray naturally stimulates your garden plants to produce more plant sugar, which is the basis for the size, production, and the flavor and sweetness of your garden produce. We recommend this product highly; plus it comes with a really good warranty.

WATERING

For most of the growing season, potatoes require about one inch of water weekly. If you're mulching, check moisture levels weekly, but you shouldn't need as much water.

If you have sandy soil, you may need to water more frequently. Mulching will help, but the water will drain downwards rather than evaporating upwards.

If you are able to, use soaker hoses or drip irrigation and make sure your soil stays wet at least 12" down.

Light watering of potatoes is virtually useless. Erratic irrigation may cause "hollow heart;" the inside of the potato will be hollow.

Reduce watering when the plants begin to yellow and die.

COMPANION PLANTING / CROP ROTATION

Alyssum attracts beneficial wasps and acts as a living mulch.

Horseradish is said to ward off Colorado Potato Beetles (I haven't tried this, but it appears to be well-founded).

Marigolds also are noted to keep beetles away from Potatoes.

Tomatoes and Potatoes should not be planted near each other as they can infect each other with early and late blight.

Potatoes shouldn't be planted in the same area for at least 4 years after they have grown in an area.

Potatoes and Winter Squash (Pumpkins, Butternut, etc.), if planted near each other, will inhibit each other's growth.

WHEN TO HARVEST

You can begin to harvest "new potatoes" when potato plants are still green - we usually wait until the plant is flowering.

Harvest your potatoes after most of the vines have died, before the soil temperature drops below 40°F, causing the starches to turn to sugar (makes potatoes lose their flavor).

Harvest just after a light frost and before the heavy frosts begin in the fall; if you can, wait a couple of weeks to let the potato skins harden.

Place shovel about a foot away from the main potato vine and dig straight down; pull back on your shovel...you should pop up a potato or two or three...repeat on the opposite side and continue down the row this way.

Be careful not to accidentally skin the potatoes as it will affect their long-range storability.

STORAGE

Don't wash your potatoes until you're ready to use them.

Store potatoes for a couple of weeks in a cool, dry area at about 55° to 60°F, then store them in a very cool, dark place - 40° to 45°F at 90% Humidity - through the winter.

The best practice for storing tomatoes is to layer newspaper between the layers of potatoes in a wooden box if you're able to buy or build them.

Jenny's Tip #3: We dug a 4' x 6' x 54" deep hole, lined it with a plywood box, and put our root crops in the bottom, covered them with about 18" of barley straw, and covered the hole with an old 3/4" sheet of plywood. It stays right about 40°F all winter in our "root cellar."

PREVENTATIVE AND NATURAL SOLUTIONS TO COMMON PESTS AND PROBLEMS

Colorado Potato Beetle:

Probably the most common pest attacking potatoes is the Colorado Potato Beetle.

This striped beetle winters in the soil, then re-appears the following spring.

Both adult and larvae beetles feed on the potato plant leaves; if left unchecked, they can defoliate the entire potato plant.

Potatoes grow fastest after flowering, so this is the most important time to make sure these beetles are under control.

Insecticides available to home gardeners are virtually powerless against the Colorado potato beetle due to insecticide resistance.

If you have a small garden, handpicking is generally quite effective (we had about six 60' rows year before last and we handpicked the beetles).

Check under the leaves and crush any yellowish-orange eggs you find.

Early varieties tend to be unaffected by the beetles as the crop is done by the time the beetles are out in any great quantities.

Another complex and common parasite is the root-knot nematode. Due to space requirements this will be discussed in the Resources section.

Flea Beatles:

Flea beetles are small, shiny black beetles that attack your potato seedlings. They chew tiny holes in the leaves, reducing plant vitality and decreasing the plant's yield.

Row covers over the seedlings is the best organic solution to keeping these pests away from your young plants. Remove when the temperatures get too hot.

Marigolds planted among your potatoes is said to deter beetles, although we haven't tried this yet (maybe this year).

ENVIRONMENTAL FACTORS

Early blight / late blight; early blight cause lesions on your potatoes and late blight causes leaf spots on potato plants.

Early blight is caused by a fungus called Alternaria solani. It causes dark, sunken lesions on the potatoes that have raised purplish edges. These can be cut off before cooking and eating as they remain mostly on the surface of the spuds.

The best preventions is crop rotation and maintaining proper soil nutrition (see Prepping Your Soil above).

Late blight is caused by a fungus called Phytophthora infestans. If there is a cool, rainy spell, late blight can spread rapidly, killing all your potato plants.

Late blight also affects nightshade family plants including tomatoes, which is why these two crops should not be near each other in your garden.

Late blight looks like water-soaked lesions on your potato plants lower leaves; these lesions will eventually kill the leaves, then the plant. It can also spread to the potato, causing dry rot.

Prevention is similar to early blight. Rotate your crops and don't plant near tomatoes. Water your plants in the morning so they'll dry out as moisture is what causes this fungus to spread.

Verticillium: this is a very information heavy topic. If you want to know more about it, go to this section on our Resources page.

Scab: a very common diseases in potatoes, is caused by a strep bacteria.

Scab appears mostly in potatoes that are grown in soils with a pH of greater than 5.2, and in drought conditions.

It mainly affects the potato itself, and not the plant. You can't really see any affect above the ground.

Scab doesn't affect potatoes in storage, and is harmless to humans.

It shows up as a lesion, but is mostly cosmetic as these potatoes can be eaten safely by humans.

If you choose scab resistant varieties, you'll likely have few issues with scab.

Don't use manure, lime or wood ash in your garden, and keep your potatoes well-watered, especially during flowering.

And of course, always plant your potatoes in different areas for at least four years.